Preparation of higher chlorides of uranium



March 7, 1950 H. G. REIBER 2,

PREPARATION OF HIGHER CHLORIDES F URANIUM Filed Sept. 13, I944 (molal rafio) Velocii'y o'F 1cm. er A gas mixhlre secofid REACT/ON PRODUCT COMPRISING URANIUM HIGHER CHLOR/DES RICH 11v 00/ 3 Fig; 1

PERCENT (BY WEIGHT) UC| IN REACTION PRODUCT o io 2o so 4o MOLAL RATIO Cl /CCl INVENTOR {1'95 2 HAROLD G. REIBER BY W4 W ATTORNEY.

Patented Mar. 7, 1950 are, 6

PREPARATION OF HIGHER CHLORIDES OF URANIUM Harold G. Reiber, Davis, Calif., assignor to the United States of America as represented by the United States Atomic Energy Commission Application September 13, 1944, Serial No. 553,924

This invention relates to the production of iranium hexachloride. More particularly, it re- .ates to the production of a mixture of higher :hlorides of uranium in which uranium hexazhloride is the principal uranium chloride con- ;tituent by the treatment of a uranium oxide- :ontaining material with a gaseous mixture comirising chlorine and carbon tetrachloride at an elevated reaction temperature. Still more par- ;icularly, it relates to a process of the aforemensioned nature in which the preferred starting naterial comprises uranium trioxide.

There is a present need for large quantities 3f uranium hexachloride. This recently discovared substance is an iridescent dark green crystal- Line material having a vapor pressure of approxinately 1 to 3 mm. Hg at 100 C. It decomposes rapidly under ordinary atmospheric conditions, e., in the presence of moist air, but is stable in vacuum and in dry air, nitrogen, helium,'and the 1 .ike, at ordinary room temperature. It is comoaratively soluble in carbon tetrachloride. Its

preparation by a method involving the dispro- JOItlOIlEtfiOn of uranium pentachloride by heatabsolute pressures of the order of 10- to 10- mm. Hg is described and claimed in the copending application by Francis A. Jenkins, Serial No. 494,447, filed July 13, 1943. However, uranium pentachloride is not as satisfactory a starting material for the preparation of the hexachloride as could be desired because the theoretical yield of the hexachloride prepared in this manner is only 54.3% by Weight (50 mol per :ent) of the pentachloride, thus indicating that the well-known compound UC15 may be represented by the formula, UClr-UCls. Furthermore, the uranium pentachloride itself must first be prepared, such as by a separate step of chlorinat ing uranium oxide. The direct preparation of uranium hexachloride from the more readily available uranium compounds, such as uranium oxide, is therefore a desideratum.

I have discovered that by passing a mixture of chlorine gas and carbon tetrachloride vapor over uranium oxides, particularly uranium trioxide, under carefully controlled conditions, I may obtain good yields of a composition com prising higher chlorides of uranium having a. high content of uranium hexachloride.

I am aware that it has been suggested previously to react various oxides of uranium with chlorine and with carbon tetrachloride vapor at elevated temperatures;

For example, Marden,--

12 Claims. (Cl. 23-145) U. S. P. 1,646,734, dated October 25, 1927, treats thorium dioxide while in admixture with carbon with a mixture of chlorine and carbon tetrachloride vapor as a bright red heat with the production of thorium chloride, ThCl4, and suggests that uranium chloride may be similarly prepared. Michael and Murphy, Amer. Chem. J 44, 384 (1910), treat various oxides of uranium with a solution of chlorine in carbon tetrachloride under liquid phase conditions, with the formation of uranium tetrachloride and uranium pentachloride. Referring to the work of Camboulives (Compt. Rend., 150, 175; 1910), Mellor, in A Comprehensive Treatise on Inorganic and Theoretical Chemistry, XII, 57 and 80 (1932), discloses that it is old broadly to react carbon tetrachloride vapor with U03 at elevated reaction temperatures, U014 and UC15 being formed. Mellor also refers (page 57) to the work of Quantin (Compt. Rend. 106, 1074 at 1075; 1888) indicating that carbon tetrachloride reacts at high temperature upon U03 to give a mixture of uranyl dichloride and uranium hexachloride, but this appears unquestionably to be an erroneous interpretation of Quantins original publication which states merely of the action of carbon tetrachloride: lacide duranium donne pareillement un mlange doxychlorure et de chlorure duranium. It may also be pointed out that Gmelin, Handbuch der Anorganischen Chemie, 8th ed., System No. 55, page 98 (1936), cites the same Quantin publication as showing the production of UO2C12 and UCLl. Finally, Rideal, J. Soc. Chem. Ind., 33, 673 at 674 (1914), suggests the preparation of uranium tetrachloride by passing a current of chlorine saturated with carbon tetrachloride vapor over a mixture of uranium oxide and sugar carbon at low red hea Uranium pentachloride is said to be produced with the tetrachloride. However, so far as I am aware, it has never been reliably reported in the literature that the treatment of uranium oxides with chlorine and/or carbon tetrachloride yields any uranium chlorides other than the tetrachloride and/or the pentachloride.

An object of my invention is the preparation of uranium hexachloride from uranium oxide.

Another object of my invention is the conversion of uranium oxide to a composition com-- prising higher chlorides of uranium that is characterized by its high content of uranium hexachloride.

A further object of my invention is the conversion of uranium oxide, and particularly the trioxide, to uranium hexachloride by a methodthat is simple and capable of close control of the reaction conditions.

I have discovered that by reacting uranium oxide, and particularly uranium trioxide, with a mixture of chlorine gas and carbon tetrachloride vapor under carefully controlled conditions, I may obtain as reaction products compositions comprising a mixture of .higher chlorides of uranium in which the uranium hexachloride content is of the order of 70 to 75% or higher by weight. As a result of my research, I have established that this advantageous result apparently depends primarily upon controlling closely the molal ratio between the chlorine and carbon tetrachloride present in thegaseous mixture employed for the reaction, and to a somewhat lesser extent upon the linear velocity with which the gaseous mixture is passed over the uranium oxide undergoing reaction. For reaction temperatures in the range of approximately 350 to 600 C., and preferably in the range of approximately 375 to 550 0., I have found that particularly favorable results are obtained when the Clz/CCl-i molal ratio is above 10, and preferably above 15, and with linear Velocities of the gas mixture of at least .1 cm. per second, .and preferably in the range of approximately 1 to 7 cm. per second.

In the accompanyingdrawing, Fig. 1 is a schematic representation .of the procedure upon which the invention is'largely based, applied to uranium trioxide as starting material for purposes of illustration. Fig. 2 is a curve showing average .results obtained upon treating uranium trioxide in accordance with the invention, and

expressed in terms of the UCle-content of the reaction product plotted :as .a function of the C12/CC14 molal ratios of the gas mixtures employed for reaction.

The feed end of the reaction tube also communicated with a source of dry carbon dioxide gas.

After placing the charge of uranium trioxide in the reaction tube situated within the furnace, and while bringing the furnace up to a reaction temperature of approximately 375 C., a current of dry CO2 was passed through the apparatus during a total period of one to'three hours to substantially completely dry the charge and to sweep out substantially all residual moisture within the system. Chlorine gas and carbon tetrac'hloride vapor were then admitted to the reaction zone and passed over the heated charge. The linear velocity of the gas mixture and the molal ratio of the components thereof were as indicated hereinafter.

Upon admitting the chlorine gas to the reaction zone at the rate of approximately 87 parts per hour and the carbon tetrachloride vapor in admixture therewith at the rate of approximately 7.1 parts per hour, corresponding to a C12/CC14 molal ratio of approximately 26.6, and passing the gaseous mixture over the charge of uranium trioxide at approximately 375 C. with a linear velocity of approximately 3.7 cm. per second, the charge of uranium trioxide was substantially completely converted into higher chlorides of uranium, the reaction product in vapor form passing over into the product receiver where it was condensed. The product recovered from the product receiver analyzed 78.4% uranium hexachloride.

The foregoing procedure with uranium trioxide as starting material was repeated, but with different reaction conditions. For the sake of brevity the procedural details are omitted, and the results of a number of representative runs are shown directly in tabulated form:

Tablel Approx. Per Cent C12, (C14 Linear Example ggg i Parts per Parts p'er i''?" i g fg Velocity, ggh;

012 001. cm/sem (Calculated) '10 87 11. 2 375 16. 8 3. 8 77. 7 8 87 17. G 375 JO. 7 3. 9 74. 4 10 v87 5. 8 440 32. 5 4. l 79. 2 8 87 17. 525 11. 1 4. 8 71. 0 10 72. "9. 2 440 17.1 3. 5 74. 6 .145 5.8 440 54. 2 6. 7 76. 5 8 43. 5 15. 7 440 6. 0 2. 3 69. 5

Having described the invention in its broader aspects, I now give more detailed examples of procedure in accordance therewith in order to assist in a'still better understanding of its various ramifications, it being understood that this is included herein for purposes of illustration rather than limitation. Parts are by weight unless otherwise indicated.

Example 1 oxygen-free carbon tetrachloride vapor to thereaction zone in closely controlled quantities..-

The results of the foregoing examples (except Example VII for reasons to be mentioned below), as well as the results of other runs under a variety of operating conditions, are plotted in Fig. 2 in terms of the weight per cent of U016 in the reaction product versus the Clz/CCh molal ratio. From the data obtained, it is apparent that the molal ratio of chlorine to carbon tetrachlorine in the gaseous mixture employed for the reaction greatly influences the uranium hexachloride content of the product obtained. It will be noted from Fig. 2 that, generally speaking, molal ratios of .C12/CC14 of approximately 10 or higher, areaction product is obtained that comprises higher chlorides of uranium in which the uranium hexacjhloride content is of the order of or better.

It will be noted that the curve has not been extended to the right sufiiciently far to include high molal ratios correspondingto that of Exampie VII. The reason for this is as follows: Although for high values of Clz/CCl-r molal ratios the percentage of UClsin-the reaction product isguitesatisfactory (e g, 76.5%.inExamp1e VII) I have found that (other things being equal) the use of high molal ratios results in substantially lower reaction rates, so that under such circumstances the reaction slows down to a relatively The total gas pressure within the system is substantially atmospheric during the course of the conversion of uranium oxide to the hexachloride as described herein. However, if desired,

impractical degree. Stated somewhat differently, 5 subatmospheric or superatmospheric pressures other conditions including overall flow rates of may be employed without departing from the the gaseous mixture remaining the same, higher spirit of the invention. molal ratios correspond to a throughput of lower Inert gases, such as nitrogen and carbon diquantities of C014 per unit time in the reaction oxide, may be admixed with the gaseous mixture zone, and since the C014 is necessary for the conemployed for reaction purposes, if desired. version of the uranium oxide, it is thus possible While I have thus far described my invention to set a preferred upper limit for the molal ratio more particularly in connection with uranium of 012/0014. Generally speaking, I have found trioxide as the charge material, uranium dioxide that molal ratios of not over approximately 35, or uranium tritaoctaoxide, U308, as well as varand preferably not over approximately 30, give ions mixtures of these oxides with each other and desirable rates of conversion. with uranium trioxide, may be employed in gen- As previously indicated, the rate at which the erally similar manner. For purposes of illustrareactant gas mixture is caused to pass over the tion, the results of two runs using uranium uranium oxide in the reaction zone apparently oxides other than trioxide are shown below in is also a factor of considerable importance, since tabulated form, the procedural details being in I have found that the use of relatively high flow all other respects similar to those described above rates results in the comparatively rapid removal in Example I:

Table II Approx. Per Cent Example g g Pa s per P 't s ger T9,?! 2 ggfifi oil con (Calculated) IX 10(U0z)--- 87 12.6 550 15.0 4.8 79.4 x 801308)... 81 15.1 540 12.5 4.8 79.4

of the reaction product from the hot reaction While it is generally preferred to use the oxides zone, thereby minimizing the tendency of the in relatively pure form in order to simplify the thermally sensitive uranium hexachloride to derecovery of the desired reaction product, this is compose. More particularly, I have found that not absolutely essential, and uranium oxide-bearthe introduction of chlorine and carbon tetraing material having a substantial content of imchloride vapor into the reaction zone in quanpurities such as other metal oxides may be emtities sufiicient to provide a total gas flow of at ployed in the process without sacrificing all the least approximately 1 cm. per second, and prefadvantages of the invention. However, it is generably approximately 1 to '7 cm. per second over 40 erally preferred to conduct the process in the subthe uranium oxide undergoing treatment, prostantial absence of any solid carbonaceous maduces optimum results. It will be understood terial in admixture with the uranium oxide or that in any case the flow rate is preferably such, uranium oxide-bearing material charged to the having reference to the particle size of the urareaction zone. Also substantially anhydrous renium oxide charged to the reaction zone, that actants, including the solid charge, are prefersubstantially no charge material is swept out ably employed. of the reaction zone and into the product receiver In order to effect a separation and/ or purificaby the flowing gases. Consequently when contion of the uranium hexachloride present in the sidering the use of relatively high flow rates, the reaction product obtained as a result of my proclast-mentioned precaution must always be obess, I may take advantage of the relatively high served, unless a high quality product is not the volatility of uranium hexachloride and subject major objective. The particle size of the charge the composition containing the hexachloride to employed for reaction in any given instance does treatment in a suitable still, in the manner denot appear to be particularly critical, provided scribed in the above-mentioned Jenkins applicaof course that the precautions just mentioned are tion or otherwise, thereby obtaining as sublimate observed. a relatively pure uranium hexachloride. This It will be understood that the chlorine gas has the added advantage that any uranium and carbon tetrachloride vapor may be introduced pentachloride present in the reaction product into the reaction zone separately or in previously contributes to the overall yield of the hexachloprepared admixture. ride. However, other separation and/or purifica The temperature employed for the reaction tion methods may be employed if desired. may be varied over a relatively wide range, par- By Way of explaining the method of analysis ticularly desirable results having been obtained of the reaction products obtained according to with a reaction temperature in the range of apthe present process, as, well as the fact that in proximately 350 to 600 C., and preferably in Tables I and II above the percentage of uranium the range of approximately 375 to 550 C. Reachexachloride is stated to be calculated, the tion temperatures toward the upper end of the normal procedure is to analyze the reaction prodranges mentioned are ordinarily preferred, howuct (a) for total chlorine content, (1)) for tetraever, in view of the resulting enhanced rate of valent uranium content and (c) for hexavalent reaction. Temperatures below or above the ranges uranium content. From each such analysis al mentioned may be employed, but in such cases the rate of reaction may become undesirably slow for practicable operation on the one hand, or undesirable side reactions may take placeto a pronounced degree on the other.

corresponding composition of the product was.

calculated assuming (1) that all the U+ was present as U014 and (2) that any oxychloride that might have been'formed as a result of side. 7 reactions was present as H0014. There'maining reases.

01 and. the, total U -were: then divided between the:twotcompoun ds UClsJand UOCl-i, and therelative amounts ofeach determined icy-simple algebraic calculations. Frequent direct analyses for U016 by subjecting an aliquot of a given react-ion product to sublimation under conditions similar to those set forth in the aforesaid Jenkins application served as acheck upon the abovementioned method of analysis, and indicated that it was sufficiently accurate (within the .ordinary limits of experimental. error) and reliable for present purposes.

Summarizing, my invention is based upon the discovery that a composition comprising higher chlorides of uranium having a high content of uranium hexachloride may be obtained by reacting uranium oxide, and particularly uranium trioxide, with a gaseous mixture of chlorine gas and carbon tetrachloride at an elevated reaction temperature lying in the range of approximately 350 to 600 0., and preferably in the range ofapproximately 375 to 550 0., with a 012/0014 molal ratio for the gas mixture of at least and with a linear velocity for the gas mixture over the charge in the reaction zone of at least 1 cm. per second, .and preferably in the range of approximately 1 to 7 cm. per second.

While I have described my invention in terms of preferred embodiments thereof, I am aware that considerable variations from the details herein disclosed might be made without departing from thetrue scope and spirit of the invention. Accordingly, the invention is to be limited only by the claims set forth hereinafter.

I claim:

1. A process forprepari-ng uranium hexachloride comprising reacting an oxide of uranium with a gaseous mixture of chlorine and carbon tetrachloride, there being at least a substantial content of each of these components in the gaseous mixture, under conditions such that a product having a high content of uranium hexachloride is produced, and recovering uranium hexachloride from the reaction product.

2. A process forpreparing uranium hexachloride comprising reacting uranium trioxide with a gaseous mixture of chlorine and carbon tetrachloride, there being at least a substantial content of each vof these components in the gaseous mixture, under conditions such that a product having a high content of uranium hexachloride is produced, and recoveringuranium hexachloride from the reaction product.

3. A. process including the preparation of a mixture of uranium ,pentachloride and uranium hexachloride comprising reactin an oxide of uraniumwith a gaseous mixture which comprises chlorine andcarbon tetrachloride, there being at least a substantialcontent of each of these components in the gaseous mixture, under conditions such that thereaction product is predominantly uranium hexachloride, and recovering uranium hexach-loride from the reaction product.

4. A process including. the preparation of a mixture of uranium pentachloride and uranium hexachloride comprising reacting uranium trioxide with .a gaseous mixture which comprises chlorine and carbon tetrachloride, there being at least a substantial. content of. each of these components in the gaseous mixture, under conditions such that the reactionproduct is predominantly uranium hexachloride, and recovering uranium hEXEtChIO-r ride fromthe reaction product.

5.,A rocessfor the preparation of uranium hexachloride comprising 'reacting an oxide of uranium with a; gaseous mixture of chlorine and carbon tetrachloride at an elevated temperature, the-gaseous mixture having atleast a substantial content of carbon tetrachloridaa 012/0014 molal ratio of at least approximately 10 and alinear velocity over the. charge in the reaction zone-of at least approximately 1 cm. per second but not soln'gh as to sweep any substantial portion of the charge material out of the reaction zone, and recovering uranium hexachloride from the reaction product.

6. A process for the preparation of .uranium hexaohloride comprising reacting uranium trioxide with a-gaseous mixture of chlorine and carbon tetrachloride at an elevated temperature, the gaseous mixture havingat least a substantial content of carbon tetrachloride, a 012/0014 molal ratio of at least approximately 10 and a linear velocity over the charge in the reaction zone .of at least approximately 1 cm. per second but not so high as to sweep any substantial portion of the charge material out of the reaction zone, and recovering uranium hexachloride from the reaction product.

7. A process comprising reacting an oxide of uranium with a gaseous mixture of chlorine and carbon tetrachloride in which the content of carbon tetrachloride is at least substantial and in w ich the 012/0014 molal ratio is at least approximately 10 andv in which the linear velocity of the gaseous mixture over the charge in the reaction zone is at least approximately 1 cm. per second but not so high as to sweep any substantial portion of the charge material out of the reaction zone, and at a reaction temperature in the range ofapproximately 350 to 600 0., and recovering uranium hexachloride from the reaction product.

8. A process comprising reacting uranium trioxide with a gaseous mixture of chlorine and carbon tetrachloride in which the content of carbon tetrachloride is at least substantial and in which the 012/0014 molal ratio is at least approximately 10 and in which the linear velocity of the gaseous mixture over the charge in the reaction zone is at least approximately 1 cm. per second but not so high as to sweep any substantial portion of the charge material out of the reaction zone, and at a reaction temperature in the range of approximately 350 170600" 0., and recovering uranium hexachloride from the reaction product.

9. A process comprising reacting an oxide of uranium with a gaseous mixture of chlorine and carbon tetrachloride in which the 012/0014 molal ratio is in the range of approximately 15 to '30 and in which the linear velocity of the gaseous mixture over the charge in the reaction zone is in the range of approximately 1 to 7 cm. per second, and at a reaction temperature in the range of approximately 375 to 550 0., and recovering uranium hexachloride'from the reaction product.

10. A process comp-rising reacting'uranium trioxide with a, gaseous mixture of chlorine and carbon tetrachloride in which the 0lz/00l4 molal ratio is in the range of approximately 15 to 30 and in-which the linear velocity of the gaseous mixture over the charge in the reaction zone is in the range of approximately 1 to 7 cm. per second, and aim reaction temperature in the range of approximately 375 to 550 0., and recovering uranium hexachloride from the reaction product.

11. A process for the preparation of uranium hexachloride comprising reacting an oxide of uranium at an elevated reaction temperature with a gaseous mixture of chlorine and'carbontetrachloride in which the-content of "carbon tetrachloride is at least substantial and in which the Clz/CCh molal ratio is at least approximately 10 and in which the linear velocity of the gaseous mixture over the charge in the reaction zone is sufiiciently high to sweep the product uranium hexachloride from the hot reaction zone without decomposition of any substantial portion thereof, but not so high as to sweep any substantial portion of the charge material out of the reaction.

zone, and recovering uranium hexachloride from the reaction product.

1 A process for the preparation of uranium hexachloride comprising reacting uranium trioxide at an elevated reaction temperature with a gaseous mixture of chlorine and carbon tetrachloride in which the content of carbon tetrachloride is at least substantial and in which the Clz/CCh molal ratio is at least approximately 10 and in which the linear velocity of the gaseous mixture over the charge in the reaction zone is sufficiently high to sweep the product uranium 10 hexachloride from the hot reaction zone without decomposition of any substantial portion thereof, but not so high as to sweep any substantial portion of the charge material out of the reaction zone, and recovering uranium hexachloride from the reaction product.

HAROLD G. REIBER.

REFERENCES CITED The following references are of record in the file of this patent:

Mellor: Comprehensive Treatise on Inorganic and Theoretical Chemistry, vol. 12, 1932, page 5'7 (Quantin: Comp. Rend., 1888, vol. 106, pages 1074-1075).

Rideal: J. Soc. Chem. Ind, 1914, vol. 33, pages 6734574, Otto Rufi and Alfred Heinzelmann, Danzig.

Z. Anorg. Chem, '72, pages 63-84 (Chem. Abst. Vol. V, 1911, page 3772) 

5. A PROCESS FOR THE PREPARATION OF URANIUM HEXACHLORIDE COMPRISING REACTING AN OXIDE OF URANIUM WITH A GASEOUS MIXTURE OF CHLORINE AND CARBON TETRACHLORIDE AT AN TEMPERATURE, THE GASES MIXTURE HAVING AT LEAST A SUBSTANTIAL CONTENT OF CARBON TETRACHLORIDE, A CL2/CCL4 MOLAL RATIO OF AT LEAST APPROXIMATELY 10 AND A LINEAR VELOCITY OVER THE CHARGE IN THE REACTION ZONE OF AT LEAST APPROXIMATELY 1 CM. PER SECOND BUT NOT SO HIGH AS TO SWEEP ANY SUBSTANTIAL PORTION OF THE CHARGE MATERIAL OUT OF THE REACTION ZONE, AND RECOVERING URANIUM HEXACHLORIDE FROM THE REACTION PRODUCT. 